Chromatography Forum

Hi Everyone,

I'm running method TO-15 (volatiles in ambient air) on an Agilent 7890/5975 GC/MS. Have only been running this system since last March so still learning new things about it. I run in SIM mode. There is an option for switching from low resolution to high in the edit SIM parameters portion of the method. The default is low and that's where I've been running. What will running in high do? I can't find anything about this in the printed or electronic manuals. I'm hesitant to experiment at the expense of losing samples and losing time. Anybody know much (anything) about this? Thanks for the help.

I am not familiar with Agilent GC-MS systems but I would guess it refers to the "resolution" of the quadrupole. At low resolution the quad is likely to transmit ions over a window of about 4 Da, while at high resolution it will transmit across a window of 1 or 0.7 Da. This should not be confused with high resolution systems such as orbitrap or FT-ICR. Running at "high resolution" on a quadrupole may improve selectivity but decreases sensitivity. Frequent users of Agilent MS may confirm (or infirm).

My MSD is a 5973 from Agilent. For this instrument the "low resolution" setting uses a 0.7-0.9 amu mass window and the high resolution a 0.5 amu mass window. For example, if you are monitoring a nominal mass of 150, in low resolution the system detects all ions in the range 149.3-150.7 and in high resolution 149.5-150.5. The outcome is that with low resolution sensitivity increases but selectivity (somewhat) decreases. I work with low resolution in most methods with no problem at all but I suggest that you try it with your analytes; sometimes it is not worth it to switch to low resolution since you don't get more sensitivity in which case I'd work with high resolution.
I advice you to check an earlier post that dealt with this topic (5973 AMU for +/- 13C-dieldrin...)